1. Field of the Invention
The present invention relates to oil injection lubrication systems for engines, and more particularly to an oil injection system for lubricating a multiple cylinder engine.
2. Description of the Related Art
For two-cycle engines, it is a common practice to mix lubricating oil with induction air to lubricate engine parts. Conventional systems typically mix oil with induction air in the same proportion regardless of engine speed. Such systems also typically deliver the same amount of oil to each cylinder regardless of the engine operating conditions. Under certain conditions, however, some cylinders of some engines require more lubricating oil than other cylinders. Furthermore, operating conditions such as cylinder resting periods, idling periods, rapid acceleration periods, or continuous speed periods often result in variations in the appropriate amount of oil required for each cylinder. Conventional systems do not provide the capability of adjusting the amount of oil delivered to each cylinder to compensate for these situations. Consequently, conventional systems suffer from problems such as smoke generated by the mixture of air and lube oil, odor, and heavy oil consumption.
Existing systems for single cylinder engines provide a solenoid valve at a discharge side of a mechanical oil pump through which oil delivery can be regulated in response to varying engine operating conditions. In these systems, however, the oil pump is typically configured to supply oil at a constant volume per crankshaft revolution. At extremely low engine speeds, an engine may require much less oil per revolution than at higher speeds. As a consequence, the solenoid valves may have to be actuated in a relatively heavy duty cycle to appropriately regulate the flow of oil at low engine speeds. Actuation of the solenoid valves draws electrical power. Consequently these systems adversely draw a relatively large amount of electrical power during low engine speed periods when it is also more difficult to generate electrical power. Still another disadvantage of existing systems is that they would require a complicated layout of solenoid valves and lines in order to be adapted to multiple cylinder engines.
In many outboard boat motors having two-cycle engines, an oil tank that supplies oil to the oil injection system is generally mounted below a flywheel on a side of the engine body. This arrangement allows only a small clearance between the oil tank and flywheel because other parts such as a fuel tank, fuel pump and oil filter are crammed into a tight engine compartment. As a result, pipes and wires cannot pass above the oil tank. Further, particularly for direct fuel injection type engines, fuel pipes and wires may have to detour around the oil tank, resulting in undesirably long pipes and wires. Longer pipes and wires are less efficient and more susceptible to damage. Prior art oil tanks are also susceptible to backflow or siphoning of the lubricating oil back into a main tank located in the hull of the boat, when, for example, the oil tank is tilted as the engine is raised out of the water.
The present invention provides an improved oil injection lubrication system for an engine, which has particular application in connection with a multi-cylinder engine.
In accordance with one aspect of the present invention, the system comprises a variable output oil pump, the output of which can be varied in relation to a throttle valve position. A solenoid valve unit, which includes a plurality of solenoid valves, regulates the flow of oil from the oil pump to each cylinder. An electronic control unit sends control signals to the solenoid valve unit to regulate the flow of oil based upon engine operating conditions in accordance with a control scheme. By adjusting the output from the oil pump in accordance with the throttle position, the volume of oil directed to each cylinder is roughly equal (i.e., approximates) to a predetermined volume of oil required or desired for a given engine speed or operational condition. The solenoid valve unit then regulates the volume flow to each cylinder through the solenoid valves to fine tune the amount of oil delivered to each cylinder (including both the combustion chamber and the corresponding crankcase section) to more precisely equal the predetermined volume, that volume depending upon the engine""s running condition.
In a preferred mode, one solenoid valve is dedicated to each cylinder. The valve circuitry is configured to permit oil flow from the oil pump to the cylinders when the corresponding solenoid valves are in an inactive state. The ECU powers the solenoid valves to temporarily close the valves and direct a portion of the lubricant flow away from the cylinders (e.g., through a line to an oil tank). By varying the closure times of the valves, the ECU can finely tune the amount of oil delivered to each cylinder in accordance with predetermined control strategies.
In accordance with this aspect of the present invention, a lubrication system is provided for an engine having a plurality of cylinders. The system comprises a plurality of oil supply pipes, each oil supply pipe being configured to supply oil to one of the plurality of cylinders. A solenoid valve unit is connected to the plurality of oil supply pipes and regulates the flow of oil to the cylinders. An oil pump is connected to the solenoid valve unit to supply oil to the unit, and an electronic control unit is connected to and communicates with the solenoid valve unit to control the operation of the unit.
In one mode, an oil supply pipe carries a flow of oil from the valve unit to a vapor separator tank for mixture with the fuel supply in order to reduce the formation of deposits on fuel injectors, lubricate the fuel system, and/or prevent corrosion.
In accordance with a preferred method of controlling oil delivery to the cylinders of an engine, the method comprises producing a base volume flow of oil per crankshaft revolution. The base volume is adjusted per crankshaft revolution to deliver an adjusted volume per crankshaft revolution. This adjusted volume is then fine tuned for each cylinder.
In a preferred mode of operation, the base volume per crankshaft revolution is supplied through a positive displacement oil pump, and the base volume per crankshaft revolution is adjusted by varying the volume output per revolution by the positive displacement oil pump. The volume supplied per revolution by the positive displacement oil pump is preferably adjusted in relation to a position of a throttle valve of the engine. The adjusted volume is then fine tuned by passing the adjusted volume through a solenoid valve.
In accordance with another aspect of the present invention, the lubrication system comprises an oil tank having a recess and a number of raised portions that allow the tank to be mounted to the engine in a compact configuration proximate the flywheel without interference while providing a passageway for control lines and fluid conduits in the recess. The oil tank is also preferably configured to have an inlet that remains above the maximum oil level to prevent backflow or siphoning of oil back into a supply tank in the hull of a watercraft.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiment which follows.